This invention relates to the field of retroreflectors, and more particularly, to lateral transfer retroreflectors and roof mirror assemblies.
Retroreflectors generally have the property of causing incident and reflected light rays to travel along parallel paths. To achieve this parallelism, a retroreflector normally consists of three optically flat reflecting surfaces, each reflecting surface positioned at a right angle to each of the other reflecting surfaces. Any departure of the reflecting surfaces from their perpendicular orientation will cause the incident and reflected light rays to depart from parallel.
Retroreflectors lose accuracy when they are exposed to external stresses. Examples of such external stresses are mass, thermal expansion or contraction of the substrate material from which the retroreflector is made, or deflection caused by curing of the adhesives which join members of the retroreflector.
A roof mirror assembly is an optical assembly consisting of two mirror panels having their reflective surfaces arranged at substantially right angles to each other. Often, a roof mirror is used in association with another single mirror panel offset from the roof mirror assembly. In such a configuration, the reflective surface of the single mirror panel is arranged to be at a substantially right angle to each of the reflective surfaces of the roof mirror assembly. Such an overall optical device is normally called a lateral transfer retroreflector because the three substantially perpendicular reflective surfaces of the three mirror panels (two from the roof mirror and the one, single panel) are essentially arranged in the formation of a retroreflector assembly, but with one of the mirror panels (the single panel) of the retroreflector assembly offset a lateral distance from the other two mirror panels (the roof mirror).
Accordingly, there has been significant development of retroreflectors/roof mirrors/lateral transfer retroreflectors that focus on the precision of the alignment of the reflective panels of these assemblies, so as to achieve the greatest degree of parallelism possible of the incident and reflected rays. When striving to construct a very accurate retroreflector/roof mirror/lateral transfer retroreflector assembly, attention will be given to reducing the external stresses that cause deflection of the reflective surfaces of the individual mirror panels upon joining the mirror panels together. Examples of such external stresses are mass, thermal expansion or contraction of the substrate material from which the mirror panels are made, or deflection caused by curing of the adhesives which join the mirror panels together or adhere the mirror panels to their supporting members.
Examples of some of these prior art retroreflectors, roof mirror assemblies and lateral transfer retroreflectors, are:
U.S. Pat. No. 3,977,765 to Morton S. Lipkins, which disclosed a retroreflector mounted to a support structure through means of applying a small amount of adhesive into the joints formed between joined members of the retroreflector and to a flat surface of the support structure.
U.S. Pat. No. 4,065,204, also to Morton S. Lipkins, which disclosed a lateral transfer retroreflector consisting of a base, a roof reflector having two reflecting plates and a third reflector. The base acts as an extension of the third reflector by attaching the third reflector to the roof reflector in the manner known to retroreflectors to produce the lateral transfer retroreflector construction.
U.S. Pat. No. 5,024,514 to Zvi Bleier and Morton S. Lipkins, which disclosed a lateral transfer retroreflector having a roof mirror of a particular construction and attached to the underlying lateral transfer member through use of three co-planar mounting pads.
U.S. Pat. No. 5,361,171 to Zvi Bleier, disclosed a lateral transfer retroreflector having a particular and different roof mirror construction than that shown in the '514 patent.
It would be desirable to provide a high-accuracy lateral transfer retroreflector that is off-the-shelf adjustable as to the displaced length between the mirror panel and the roof mirror and also having a less temperature-deviant assembly and mounting of the roof mirror and mirror panel.
It would be further desirable to provide still further constructions for a high-accuracy roof mirror assembly to be used in lateral transfer retroreflector assemblies and other optical assemblies, whereby the roof mirror assembly is a separately constructed and assembled unit that maintains the reflective surfaces of its two mirror panels in as near perpendicular orientation as possible, while allowing assembly of this roof mirror assembly to such other structure without substantially affecting the alignment of the reflective panels of the roof mirror assembly.